The invention discloses a scale removal device for a flue and belongs to the technical field of flue cleaning equipment. The scale removal device is characterized in that a liquid outlet pipe (24) isconnected at the bottom of the flue (1); the liquid outlet pipe (24) is arranged on one side, opposite to a smoke inlet (101) of the flue (1); a flow guide plate (25) is further arranged at the bottomof the flue (1); the lower side of the flow guide plate (25) is rotationally mounted on the lower side of the liquid inlet end of the liquid outlet pipe (24); the upper side of the flow guide plate (25) is higher than the smoke inlet (101) all the time; and the height of the upper side of the flow guide plate (25) and the height of the lower side of the flow guide plate (25) are larger than the width of the flue (1). By the aid of the scale removal device for the flue, the ventilation effect of the flue is guaranteed, fire dangers caused by open fires in the flue are avoided, a cleaning liquid can be guided to the liquid outlet pipe by the flow guide plate and flows out of the liquid outlet pipe, meanwhile, the smoke inlet can be sealed, when the flue is used normally, the flow guide plate swings to seal the liquid outlet pipe, smoke can be prevented from overflowing the liquid outlet pipe, and the cleaning liquid can be prevented from entering the smoke inlet.